HV alternator ?'s

[bob g]

so therefore got to thinking maybe there are others here that have or are working with the higher voltage systems.

to preface my questions a little personal historical perspective

i have a very good wind resource, that is approx 300 ft from my homesite which is further down the hill face. so clearly a 12 volt system would be a poor choice, a 24 only slightly better and 48 still not good enough.

i will have a segmented system

system A will be a 24volt system, possibly 48 volt (depending on the results of some testing i am working on in regard to alternator efficiency)it will be charged primarily via solar, with an engine driven alternator as back up. inverter capacity will be about 3kva peak. this system will be the one that does the bulk of load service for the house.

system B. will be the 120 volt system, and will be charged via the windgenerator

it will feed another inverter that is rated at 12.5kva, this system will provide for

intermittent and heavy loads such as well pump, and other large hard to start loads

that don't run very often or for very long, perhaps an hour a week on battery and longer if there is sufficient wind power available.

i am thinking i would like to do a windgen in about the 2kwatt class, 120volt dc

but generate and transport as ac and rectify at the house.

my power winds are in the area of 15-20mph for the sake of information.

now my questions

approx how large a machine?  would a 10-12 footer deliver 2kwatt in 15-20mph winds?

and are the higher voltage machines more efficient in practice?

i realize that 24 and 48volt machines are inherently more efficient than the 12volt units, is there significant increases in alternator efficiency going from 48 to 120volts.

oh yes, lest i forget

all power, batteries, inverters etc will be in a detached power house, so that i do not have to worry about NEC code limits of 48vdc. there is no county inspector or permits needed, and there will be no grid connections or considerations made by a power company.

thanks

bob g

[ghurd]

Some of the numbers seem out of kilter to me.  I could be way off.

Like the hard to start loads and 12.5kva peak inverter for an hour a week.  1800wh/day.

And 2kw in 15-20MPH wind.  An hour at 15-20 would cover the whole week.

Looks like it does not need anything near 2kw at 20MPH.

Hard to start items like a pump do not usually take near the same power to run.

Figure they take 1/3rd of starting power?  600wh/D?

Just seems like the wh/d is way off.

G-

[bob g]

i am sure my numbers are way off, i just wanted to kick out enough info so as

not to have 6 guys asking for stuff that really doesn't answer the question.

so maybe i should boil it down to specific's

is there as large an increase in overall system efficiency going from 48 vdc up to 120vdc as there is going from 12 volts to 48volts?

does a similar increase in efficiency take place with the aircore alternators as well?

quite frankly most of what i need to do i can cover with a very modest system, with solar and never even mess with a tower up on the hill.

so the wind thing would be a redundant power source most likely.

bob g

[ghurd]

I do not see iron/air core coming into it.  At least not much at this scale.

It is still I^2xR in the coils and line.

P-N junction loss will be far less %.

Higher voltage is better.

Battery cost and replacement could get out of hand.

[scottsAI]

bob g,

Higher voltage will save you in wire cost for 300 ft.

Current is lower, use thinner wire. Calculated using 120v at 20a

14. awg 31volts drop 25% loss, used single phase to calculate. 3 phase 26v.
    
12. awg 20volts
    
10. awg 12.3v
    
12. foot wind turbine: assuming 75% blades, 80% gen => 36% over all efficiency.
    
15. mph = 698w, 20mph = 1656w. Not making your numbers.
    
14. foot wind turbine same assumptions.
    
15. mph = 951w, 20mph = 2254w.
    
16. foot: 15mph = 1242w, 20mph 2945w
    
17. foot: 15mph = 1402w, 20mph 3324w, 17mph = 2041w
    
17. foot seems to meet your goals. (17mph wind).
    
    

Have fun,

Scott.

[pvale]

Unforunately, making the jump from 48V to 120VDC causes a 4-5fold jump in device prices. By the time you get to 120VDC, just getting switches to interrupt current requires a magnetic or air blast device to quench the arc. Relays must open their contacts wider to make sure the arc is quenched. Don't attempt to use normal AC rated light switches, they'll burn up in short order. I work in the power field, and some companies set up 120VDC battery banks as backups in substations to trip devices in the absence of AC power. A lot of them will run at least a few bulbs in the control building from the battery bank to ensure they have light in a power failure. While they can use normal 120V incandescent light bulbs, the switches to them are old really clicky units rated for 120VDC. One of the guys told me that those switches were $30 apiece. Same problem with fuses. Check the DC rating of some of the cartridge fuses rated 250VAC, and you'll see they are rated for no more than 50VDC. You can buy fuses rated for 120VDC for a reasonable price, but small molded case circuit breakers for 120VDC service are very expensive. That's why all of the systems I've seen used a fuse panel to supply 120VDC loads.

If you already have this 12.5kw inverter, you are kind of stuck, otherwise I would be content to go no higher than 48V. Just remember, the care in wiring at 120VDC is is even wore than 120VAC wiring. The most graphic example I saw of the dangers of high voltage DC was in Homepower magazine some time back, with a solar installer holding a couple of wires in his hands, and 1-2 Fat arc running between them form a ~250VDC solar array. You might should think about talking to a solar installer that installs grid tie arrays. From some of the pictures I've seen of installations, the cut-off enclosed switch they use for the DC from the array seems not to be a normal disconnect commonly used on AC. I would stay away from high voltage DC setups if I had any choice in the matter.

[dnix71]

Living well offgrid means using less power. It would be a lot easier to replace the well pump with a dc submersible, if it's only for household use.

http://www.etaengineering.com/waterpumping/well_pump.shtml

The 24v Shurflo here uses 100 watts max, and will handle deep wells. Pumping it a gravity tank is easy.

DC lighting is every bit as good as ac. You can use automobile shop lights without an inverter.

http://www.ablamp.com/12vdc_solar_lamp_cfl.html   has 6/12/24 volt dc compact florescents with standard Edison light socket bases.

Can you give us a short list of what you plan to power from batteries?

[ghurd]

Hey pvale,

How goes it?

Got a good pic of DC here... because Roy lost his lighter?

http://www.fieldlines.com/comments/2009/2/4/20452/86201/5?mode=alone;showrate=1#5

Somebody needs to smack him til the ink falls out for doing that, but I digress.

G-

[bob g]

i am aware of the perils of working with high voltage dc, and have all the very heavy duty double break contactors needed to do the switching.

the battery and inverter system will be sized to cover the load long enough for the

genset to start, warm up, and then the  load transferred to it. some loads will be so short in duration that the engine will not be called on to start.

most of those loads are shop related, items such as heavy grinders, welders, plasma cutters, that sort of thing. if i need a weld that takes 15 seconds or so, the inverter and batteries cover that load, if on the other hand the load is determined to be longer in duration the genset is called on to start up and take over the load.

i have been working with this scheme for some time now and it works very well

on a smaller scale i can start a refrigerator with a 3kva inverter, but once started

the load drops to a small fraction of the capacity of the inverter, which puts it in

a less efficient range. however

if i start the load on the 3kva inverter, and once started switch over to a 1kva inverter, i can cover that load and do so in the more efficient range of the inverter. the net result is higher overall efficiency as well as redundancy which is never a bad thing.

it takes some load managment, but that is doable with microcontroller tech pretty easy.

anyway getting back to the question at hand,

are 120vdc wind gens appreciably more efficient than 48volt machines?

(neglecting concerns with transmission line losses)

anyone built and flying a higher voltage windgenerator?

thanks guys

bob g

[Dave B]

Bob,

  I have been running my 16' axial with stator wired for  3 phase 100 VAC @ 300 RPM for over a year. Sorry I can't report on this as rectified DC as I have been heating water direct AC. 8 Gauge 3 wire down the tower 90' to the external panel and disconnect then underground 6 Gauge 3 wire to my panel and breakers inside about another 150'.

  I am no expert for sure but I have to believe that the frequency also plays into the efficiency factor. I am running more magnets and coils than most for this size machine (20x2) mags 15 coils on 16" rotors and if I ever build another high voltage machine of the same size I would elect to go with even more smaller magnets (28x2) and fewer turns with 21 coils with the same size rotor.

  Just what I have experienced at least with the AC side of your high voltage DC plans. Producing higher voltage AC AND at higher frequencies has worked very well for me. Go for it and break the norm.  Dave B.

[Dave B]

Bob,

  I forgot to add that my loaded output at 300 RPM 100 VAC exceeds 3 KW in approx. 20-25 MPH winds. This with 16' diameter (Gottigen 222 profile) blades and quite a bit of magnet clearance to the stator of nearly 1/4" each side. This to help with start up as I am direct wired no controller. 300+ RPM sure seems fast for 16' but I have run nearer 400 RPM while testing and things seem smooth but the noise starts to pick up. Very happy running at 200-300 RPM and fully furling about 350 RPM near 25 MPH winds.  Dave B.

[Flux]

Alternator efficiency in theory is not affected by voltage. System efficiency is.

It can be very difficult to design high efficiency alternators for low voltages especially for larger sizes and eventually the need to use multiple parallel circuits does present practical limitations. If you can deal with these limitations there need be no difference in efficiency for any voltage if you keep it ac.

Once you introduce rectifiers then the rectifier loss is a constant factor related to current and the higher voltage systems will see a much smaller rectifier loss, but over 24v it becomes fairly small.

Cable loss to the machine is a different thing and can only be kept low in a low voltage system by using thick and costly cable.

The alternator efficiency thing is really a bit of a red herring because if you load the thing conventionally without some form of load matching you need to limit the overall system efficiency to below 50% to keep the prop somewhere up on its power curve.

From my experience with a conventional direct loaded scheme 300ft at 2kW is fairly practical at 24v, the initial cable cost will be high if you buy it new but the insulation requirements at 24v is minimal and reclaimed cable works fine and you can parallel up what you can get.

Obviously 48 or 120v will cut the cable cost to a lower figure.

I tend to agree with some of the others that 120v is a challenge and is only suitable for those with experience and really know what they are doing. If you are competent and can get the dc switchgear and you are very careful handling the batteries then the higher voltage has some advantages along with its snags.

I think that inverters for 120v will be tricky and you are into a very specialised field but for lighting the conventional HF fluorescent inverters work on dc ( at least the ones we have here in Europe).

Now look at it another way, go mppt and things change. If you go this route even at 24v the alternator efficiency can be pushed right up ( at a cost of course) and the transmission at full power will be up to 100v so the line loss becomes small. The same applies to 48v and the line losses will be marginally lower. You will also have less loss to inverters and things with heavy load on the battery side for a given cable cost.

I don't think there is a mppt controller available at the moment that will handle an alternator starting at 120v at cut in but it may be possible to do it if you keep within the converter peak voltage rating.

What you need and what you feel comfortable with are your choices but the alternator efficiency alone is not the issue. If you don't adopt mppt in some form then worrying about efficiency is pointless, at least from the alternator point of view.

I regard 12v as a dead duck for any reasonable size system, 24v may be ok at 2kW and with mppt even the 300ft cable run would be no real challenge.48v will do the job easily with no problems. If you want to venture to 120v and feel capable of dealing with it again it will be fine for conventional direct loading but you may not be able to use mppt with the real advantages of efficiency if that is the issue that bothers you.

Flux

[bob g]

Flux:

thank you for you comments, as for load matching i have been a proponent of such

going back many years now. The thought first occured to me back in about 2001 when after reading about issues with mismatched alternators to loads and how it results in heat as a predominant product (at that time in a significant amount of cases in home built machines).

the problem was no one was much interested in, or knew much about building a buck converter, much less an mppt,,, and while i could theorize about the benefits of load matching, i too had no clue how to do a buck converter let alone mppt.

its taken several years of diggin and study, after which i now know how a buck converter operates and how to design and build one, i also know where to find industrial sized components such as power mosfets and igbt's to do the heavy switching.

wanting a more sophisticated control i learned microcontroller useage and programming and now see how i can control a buck converter in an mppt fashion of sorts.

so the bottom line for me is, i gotta give it a go, build the thing, and work out the kinks, get it working and then refine it.

working with the higher voltage has several advantages, lower losses being the most appararent, and lower current being easier to switch/convert.

Because windpower will not be the "end all" and "only" source of power at this location, the ability to work on applying load matching/mppt control seems like a most interesting project to me.

if the load matching converter can be made to work to convert power to charge a 120vdc bank it could also be used to convert the same source power to charge either the 24 or 48 volt bank as well. that would seem quite useful in my opinion as well.

thanks again

bob g

[bob g]

DaveB:

thanks for the description of your genny

i have been thinking along the lines of a 20' diameter alternator

i think i would like to get to 24 poles maybe more.

although likely not a dual magnet aircore design, but probably go back and

do one based on the Torogen design from several years back.

i have to build an alternator, and if i am going to do it, it may as well be the

Torogen.

bob g

[dnix71]

You can weld directly with batteries. That's how it was done before there was a grid.

http://www.instructables.com/id/Golfcart--Welder/

24-36 volts is all that's needed. Long cables help to limit current, since you don't have fancy amp dial swithes doing it that way.

http://www.readywelder.com/  The military uses these off the shelf MIG battery powered welders.

[scottsAI]

Thanks dnix71, you got me totally distracted wondering around for hours looking at many links for DC and AC welders.

Need to get welding rods!

Have fun,

Scott.

[bob g]

i realize i can weld with batteries, but find it hard to want to go that route

when i have several commercial grade units of various technologies

i can already power the welders just fine, just wanted to work toward a higher voltage dc system.

what i am wondering is whether there is hesitancy to higher voltage for sound reasons or whether it is just fear of the unknown?

after all there was a time when everyone was all over 12volt systems and couldn't imagine why anyone would want to go all the way up to 48volts

there was some issue brought up with the dangers of switching high voltage dc from a wind gen, when clearly all one need to to safely switch is do the switching on the ac side of the rectifier bridge. common ac contactors can handle that duty without much trouble at all.

it would appear from the responses received, there is not much representation in the high voltage arena?

Dave looks to be using 100vac to heat water, and so far no one else has stepped up

with similar.

i will give this more thought, perhaps it is best to stay back at the 24 or 48 volt level and work around that.

thanks guys

bob g

[oztules]

Time to put the hand up I guess.

I run 2 systems concurrently off the one poor windmill. I have plenty of wind.

First is the electric vehicle. It is 36 volts. It runs off the nominally 48v 4m mill, which stalls limits it very considerably... but still put out 1.5kw in peaks, and 300-500w generally.

When it is charged it can divert to the 96V system. I found a circuit board (and nothing else) down at the tip. It turned out to be a 96v 2000VA pure sine wave ups. After patching up the broken board, and replacing a few fets, it worked perfectly.

So buy using rubbish dump quality batteries at 96v (108v mostly) the mill (48v) drives the batteries very well. They peak at 4.5kw at about 110v, 40 odd amps.

When it runs the house, it easily drives 2 freezers, a big dual door fridge(inc ice maker), the TV, the computers and the  water pressure pump, lights... and well everything except the stove, and hot water and the big microwave, or the 2400w kettle.

Mostly it does this on between 4-6 amps at 108v. (I only measure the amps,... I would have thought 2 freezers, a fridge and the little tv would draw more than this... but apparently not).

I have noted several things.

Lousy batteries that wont work in a 12v/24v system any more @50-100 amps, work just fine in a HV system where they are expected to only drive 1-10 amps.... no problem for marginal batteries..... means cheapies from the tip work well for HVdc

Freezers and fridges are no problem to start, and in fact start better when there is already 1 running. (I guess the running rotor acts as a current source for the second one to start. The capacitors in the HV 96v inverter seem to withstand the 20A surge much better than 12v 200a surges... surprise surprise.

HVDC..... I use no switching in the DC circuit, so can't comment on the fear surrounding this subject. I decided to use no  DC switching as it is not necessary.

All switching is done on the HVAC side of things... either the 240vac from the inverter (ie in the house circuit), or the 110vac 3ph from the mill. I don't understand all the excitement. I use big 150A anderson plugs to connect to the inverter DCinpuit from the batt bank.. no switches, and the same plugs to connect the EV to the mill.

I would not go back to Low voltage DC.... seems so stupid in every way.

A HV system has every advantage, and no obvious disadvantages. Use the battery bank on a proper plug connection. When disconnected. this gives no load or complete circuit when wiring it up, so very small chance to get caught between potential... there is none.

When wired up, then plug it in... this completes the circuit, now all battery connections are HOT, but before plugging into a load, are basically benign.

Don't use DC switches, and no arcing is possible.

Run your dump from the wild AC side of the rectifiers... triacs are cheaper and tougher than FETS..... and you can zero cross switch them if you feel like less noise.

If you are going to use relays, they will need only be little AC ones... 100v@20A will be overkill. The relays from microwaves will do the job no problem. Solid state ones are good to go as the currents are quite within the bounds of normal consumer gear. Remember, we are only switching the AC side.

The AWP over here is a 240vac nominal mill. There are no problems with HV AC up the pole (up to 600v sometimes). Transmission is simple stuff at these voltages.

All the HVDC problems outlined in other posts are from trying to use HVDC like HVAC, or LVDC.... there is no reason to use it that way, and so avoid all the problems in the first place... HVDC is a slightly different animal, so treat it differently.

Use care but I see no need for blind fear.... I'm still here.

............oztules

[wdyasq]

Bob,

At one time I discussed a higher voltage alternator with high pole count. The idea was to get the operating frequency in the 35-80Hz range where it could be transformed.

This was to be a large system. The distance from the turbine to the battery house was ~1/4 mile.  To transform and rectify we planned on using a 240/480 volt three phase forklift transformer. This would knock the high AC voltage to a charging range. It would also allow for a 'dual range' transforming. for lower voltages the 240V windings could be used and at a certain frequency/voltage one would switch to the higher windings. This would allow one to better match the alternator.

I think I have described enough where you can imagine the process and idea.

Ron

[oztules]

Ron, thats how the AWP works over here at Jamies place. It is 30 pole 240v. It is a great flexible system... way to go I feel.

If you change battery voltage, then just change output transformer configs. All dumping and over correction happens at the wild ac side of things... simple low current stuff for high power results.

..........oztules

[bob g]

thanks for the input and experience.

your observation in regard to batteries at higher voltage is valid

one doesn't need as heavy a battery with higher voltage as he does with low voltage

just need more of them

in theory it should work out the same, but in practice

the idea that a battery that might not be able to deliver 50amps for very long

might be able to do 5amps for a very long time relatively speaking.

thanks again,, more to consider and think about

bob g

[dnix71]

If you go over 60 volts there are code and insurance requirements that make experimenting "illegal." I live in a rental, so I need to keep what I do under the radar. I cannot put up a windgen large enough to make more than a few watts and my panels are on the ground instead of the roof.

Another issue is money. I cannot make electricity for less than I can buy it. This isn't about "sticking it to the man." I live in south Florida. We go for extended periods without electricity and access to motor fuels following major hurricanes. 12v and 24v appliances are common and cheap. People live in their cars and trucks these days, so almost any home appliance exists in a mobile version. The 12v Engel fridge I use inside will go with me if I have to leave because of a storm.

If you can't get gas or diesel after a storm, owning a big generator doesn't have much value and a grid-tie system doesn't work if there is no grid to tie it to. It was 45 days before the poles and wires were replaced after hurricane Andrew, and 30 days after Wilma. There is no wind gen I could build that would stay up in 160 mph winds (Andrew) or 120 mph (Wilma). We don't get floods or earthquakes here, just brush fires and big wind.

In the 'hood where I live, esp. after a major storm, you don't want bling because it makes you a target for theft. One of my neighbors had a gas gen running after Wilma and woke up after noticing the lights were out genny sound getting dimmer. Someone was walking off with it still running at 2 am. He shined a high powered light on them and they dropped and ran.

When we get another storm, I'll have lights, a fan, cold water from a small fridge and my computer and dsl box will work, so if the phone lines are still up (like after Wilma) I can send and receive email. 12 volts is simple, save and off the shelf backup.

[bob g]

i can certainly sympathize with your plight with theft

my smallest prototype trigenerator tips the scales at 1200lbs, so the thief better bring help.

as for keeping under 48 volt nominal for codes, insurance and all that

i don't have much concern for any of that due to the fact that all power equipment will be in a detached "fireproof" bunker, that no one lives in.

codes don't cover what is inside a steel can, and where folks don't habitate.

while it is true that one cannot generate power for what one can buy it for, their is a certain sense of freedom knowing you have it done yourself, that to me has a certain value in and of itself.

if i can generate for 24 cents per kwatt/hr, and buy it from the grid for 12 cents per kwatt/hr, well the extra 12 cents per is well worth it in personal satisfaction.

besides if i generate power myself, there is not much anyone can tell me about how, when, what etc,  i do it or use it.

also i have to believe that in each guy here on this forum is a deep down need for his own menlo park or telluride.

i have waited nearly 40 years for mine, and now with my youngest only 2 years away from graduation,, i can start applying all the idea's, theory, projects, Junqu'e

that i have collected all these years, and actually take a stab at setting up my frankensteins laboratory.

why not? can't think of anything i would rather be doing

bob g

[Dave B]

Oztules,

  Great to read your reply and explain your projects as well as helping many of us learn from your own experience.

  There are many with opinions of their own based on their own knowledge of a familiar system. Many opinions can sway toward the negative when a new or less familiar approach to doing things is presented.

  Your very direct and clear explanation of handling the "objectives" of other's opinions on HVDC indicates clearly that you are doing what you want and letting us understand how and why besides.

  Thank you for posting and helping myself and others understand that knowledge (and safety) are the keys to taking this HV road less traveled.

  I'm sure there are many times when you read, smile and carry on ... this I understand.  Dave B.

[TomW]

bob;

also i have to believe that in each guy here on this forum is a deep down need for his own menlo park or telluride.

At the core, that is very true for me. My wife doesn't "get" it but tries not to interfere she understands its a guy thing. Some deep seated genetic drive involved.

I feel for the guys stuck in an apartment unable to play at this stuff except on the kitchen table.

I am often intrigued by the changes this board has gone through from early wooden alternators at 12 volts to giant machines [by those standards] at high voltage like Dave B has done. Even a few VAWT showing up making power.

All great stuff. Lots of fun being generated, too.

DonC is building a 96 volt system, including an inverter.

Funny he has not chimed in on this but he has been absent from IRC the last week so he must be busy.

I am a bit leary of the HVDC myself but then I don't use explosives for fun any more, either!

Good luck with your project. Really interesting stuff.

Tom

[scoraigwind]

wow this is a long discussion.  But I think this is the right spot to comment that I have worked with 110 volt and 120 volt DC systems for may years and seen only some minor switching issues with cheap switches.

Here in the UK there are tools available for 110 volt AC operation and the good ones will run off battery, although speed control is often compromised.

This voltage is ideal for long wire runs, but do be careful with high voltage stators as they can produce scary voltages if they run away unloaded!

High frequency is great for transformers but otherwise I don't see any great advantage at all.